1. Field of the Invention
This invention relates to a hub for use in a power transmission apparatus having a function of damping vibration and absorbing shock during power transmission.
2. Description of the Related Art
Generally, a compressor for an air conditioner system of an automotive vehicle includes a power transmission apparatus for receiving power from an external source, such as an engine via a pulley and belt, and transmitting it to the input shaft of the compressor through a hub.
A conventional power transmission apparatus of this type is disclosed, for example, in Japanese Unexamined Patent Publication No. 2006-258109. This power transmission apparatus is shown in FIG. 4. Power transmission apparatus 11 has cylindrical bearing support unit 15 projected toward the front side (left side in FIG. 4) from compressor housing 13. Pulley 19 is supported through bearing 17 on an outer periphery of bearing support unit 15 and driven through a belt or the like by a power source such as an engine.
Input shaft 23 of the compressor is supported through bearing 21 on an inner periphery of bearing support unit 15. Inner hub 27 of hub 25 is screwed to input shaft 23, and cylindrical portion 29 formed of an elastic body is arranged on the outer periphery of inner hub 27. Outer ring 31 extending rearward (right side in FIG. 4) from cylindrical portion 29 is arranged on the outer periphery of cylindrical portion 29. Outer ring 31 is fitted in annular depression portion 33 formed on the front side of pulley 19.
First hub-side engaging portion 35, having depressions on the outer periphery thereof, is formed on the outer periphery of the rear-side portion of outer ring 31. Second hub-side engaging portion 37, having depressions on the inner periphery thereof, is formed on the inner periphery of the rear-side portion of outer ring 31.
A radially outward surface of depression portion 33 of pulley 19 is formed with first pulley-side engaging portion 39 adapted to engage first hub-side engaging portion 35, while the radially inward surface of depression portion 33 is formed with second pulley-side engaging portion 41 adapted to engage second hub-side engaging portion 37.
In this power transmission apparatus, torque transmitted from the power source to pulley 19 through the belt is transmitted to first and second hub-side engaging portions 35, 37 from first and second pulley-side engaging portions 39, 41 thereby to rotate input shaft 23 and thus drive the compressor. In this transmission process, the function of damping vibration and shock is carried out by cylindrical portion 29 having an elastic body.
In recent years, there is an increasing demand to reduce vehicle noises, and in order to reduce the noises, a spring constant of an elastic body is required to be smaller. To reduce the spring constant of the elastic body, cylindrical portion 29 of hub 25 formed of the elastic body is required to be increased in the radial direction.
However, due to space limitation, cylindrical portion 29 of hub 25 cannot be increased in the radial direction. If the spring constant of the elastic body is reduced without changing the outer diameter of cylindrical portion 29 of hub 25, the durability of the elastic body would be lowered thereby.
On the other hand, in order to increase the outer diameter of cylindrical portion 29, it is necessary to bend inward the tongue-like reinforcing portions, instead of bending them outward from outer ring 31 (as FIG. 7 in Japanese Unexamined Patent Publication No. 2006-258109). If the tongue-like reinforcing portions are bent inward, stress and strain are concentrated at the root of the cylindrical rubber portion of the engaging portion, and the strain would be further concentrated if the axial distance is shorten between the root and the reinforcing portion, thereby resulting in reduced durability.